Many companies and other organizations operate computer networks that interconnect numerous computing systems to support their operations, such as with the computing systems being co-located (e.g., as part of a local network) or instead located in multiple distinct geographical locations (e.g., connected via one or more private or public intermediate networks). For example, data centers housing significant numbers of interconnected computing systems have become commonplace, such as private data centers that are operated by and on behalf of a single organization, and public data centers that are operated by entities as businesses to provide computing resources to customers. Some public data center operators provide network access, power, and secure installation facilities for hardware owned by various customers, while other public data center operators provide “full service” facilities that also include hardware resources made available for use by their customers.
The advent of virtualization technologies for commodity hardware has provided benefits with respect to managing large-scale computing resources for many customers with diverse needs, allowing various computing resources to be efficiently and securely shared by multiple customers. For example, virtualization technologies may allow a single physical computing machine to be shared among multiple users by providing each user with one or more virtual machines hosted by the single physical computing machine. Each virtual machine can be thought of as a software simulation acting as a distinct logical computing system that provides users with the illusion that they are the sole operators and administrators of a given hardware computing resource, while also providing application isolation and security among the various virtual machines. Furthermore, some virtualization technologies are capable of providing virtual resources that span two or more physical resources, such as a single virtual machine with multiple virtual processors that spans multiple distinct physical computing systems.
Various types of distributed network-accessible services may be implemented using virtualization technologies by some providers. In many cases, as the workload for a given service increases, numerous server components may be instantiated using respective virtual machines at selected hosts within one or more large data centers. Such server components may be configured to respond to service requests received from numerous client components of the service, which may in some cases also be instantiated at virtual machines executed at various hosts at the data centers. In order to support scalability of the service, intermediary nodes such as load balancers may often be employed between the clients and the servers. In such environments, a given request from a client may first be transmitted over a network connection to a load balancer, and then forwarded from the load balancer to a selected server component of the service. A response to the request may follow the reverse pathway, again involving at least two network hops. The customer of the service may typically be allowed little or no control with respect to the selection of the specific hardware devices used for the server and client components. Depending on the component placement policies in use for various services, it may sometimes be the case that a client component and a server component with which the client component interacts are both instantiated at the same host, or at a nearby host located on the same rack or in the same data center room. Such nearby placements of interacting components may sometimes provide opportunities for more efficient inter-component communication than is possible using the more traditional request-response pathways involving intermediaries such as load balancers.
While embodiments are described herein by way of example for several embodiments and illustrative drawings, those skilled in the art will recognize that embodiments are not limited to the embodiments or drawings described. It should be understood, that the drawings and detailed description thereto are not intended to limit embodiments to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope as defined by the appended claims. The headings used herein are for organizational purposes only and are not meant to be used to limit the scope of the description or the claims. As used throughout this application, the word “may” is used in a permissive sense (i.e., meaning having the potential to), rather than the mandatory sense (i.e., meaning must). Similarly, the words “include,” “including,” and “includes” mean including, but not limited to.